slapos/testing: ignore ssh-keysign in check_software

ssh-keysign is not readable by everyone so we cannot do "ldd" on it:

$ ls -al /opt/slapgrid/shared/openssh/f79ee5e4e4573183783541f2ad9133e8/libexec/
total 1332
dr-xr-x--- 2 slapsoft slapsoft     90 Jul 12 22:10 .
dr-xr-x--- 7 slapsoft slapsoft    131 Jul 12 22:10 ..
-r-xr-xr-x 1 slapsoft slapsoft 145560 Jul 12 22:10 sftp-server
-r-x--x--x 1 slapsoft slapsoft 506208 Jul 12 22:10 ssh-keysign
-r-xr-xr-x 1 slapsoft slapsoft 366736 Jul 12 22:10 ssh-pkcs11-helper
-r-xr-xr-x 1 slapsoft slapsoft 338064 Jul 12 22:10 ssh-sk-helper

slapos/testing/check_software.py

@@ -115,6 +115,8 @@ def checkSoftware(slap, software_url):
       # Python libraries lacking an rpath; these are not actually used
       # by Chromium itself
       '*/.vpython-root/*',
+      # this library is not readable by group/other
+      '*/libexec/ssh-keysign',
   ))
 
   software_hash = md5digest(software_url)